Re: [APD] Don't Drink Distilled Water [SAFETY] (was "Storing large amounts of RO water")

["Andrew McLeod" <thefish at theabyssalplain_freeserve.co.uk>]

On Sun, 26 Feb 2006 22:01:38 -0000, Jerry Baker <jerry at bakerweb_biz> wrote:

> Yes. That's why it's chemical name is hydrogen hydroxide (if you use
> standard nomenclature). It is a hydrogen cation and a hydroxide anion.
> The theory is that they tend to constantly associate and dissociate
> while in liquid form. That means at any given time a large number of
> cations and anions are floating around loose which enables water's
> notorious power as a solvent. pH is a measure of the ratio of H+ cations
> to OH- anions.

Actually I think it is purely a logarithmic measure of the concentration of H+ (actually generally present as hydroxonium, H3O+, since the single proton is too reactive to exist independently for any length of time). Adding OH- will reduce this concentration, but it isn't part of the calculation AFAIK.

Water is a very poor acid/base so only a very small amount of it dissociates. It is not bonded ionically (as in a positive hydrogen ion and a negative hydroxide ion) but covalently; electrons are shared between the oxygen and the hydrogens and no charges are exchanged. Both the hydrogens are exactly equal.
Water is actually a universal solvent, again AFAIK, since it contains:
a) lots of polar molecules
In a water molecule, the oxygen pulls the electrons a little bit away from the hydrogens making the oxygen 'end' slightly negative and the side with the two hydrogens slightly positive (water is not H-O-H in a straight line, but is 'bent' (that IS a technical term apparently) so that there is an angle of less than 180 degrees between the two hydrogens). As a result, the negative end of water can be attracted to positive ions, and the positive end to negative ions, releasing energy. This allows water to surround and dissolve ionic solids such as a wide variety of salts, acids etc.

and b) hydrogen bonding
Oxygen has six electrons. A full 'shell' is eight electrons. It shares two with the hydrogens, one each, in return getting a bit of the hydrogens electron and sort of filling the shell. This is the oxygen-hydrogen bond (the sharing of electrons). This leaves two electron pairs, so that the oxygen has four 'things' spread fairly evenly around it - the two bonds, and the two electron pairs (this is why a water molecule is bent). The strong 'electronegativity' (ability to attract electrons) of an oxygen in one water molecule attracts the electron cloud around a hydrogen atom a little bit, releasing energy. This allows water to dissolve a wide variety of organic compounds with an active group containing some sort of electronnegative atom e.g. oxygen, fluorine, nitrogen. Examples are alcohols, organic acids, sugars, most biological organic compounds...

-- 
Andrew McLeod
thefish at theabyssalplain_freeserve.co.uk

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